1. Field of the Invention
This invention relates generally to the apparatus and method for disrupting vein valves in a mammal.
2. Discussion of the Prior Art
It is well known that the vascular system is relied on to nourish the cells of the body and to remove waste materials from the cells of the body. More specifically, the arteries of the vascular system convey oxygen and other nutrients to the cells, while the veins of the vascular system return the blood and waste materials from the cells to the lungs, liver, heart and other organs of the body. Since the flow of blood from the extremities is generally upward, this return flow of blood in the veins must work against the force of gravity. To assist with the return flow, veins commonly include several valves which permit a flow of blood in the upward direction while inhibiting a flow of blood in the downward direction. Thus, the vein valves in their normal state aid in moving the blood in an upward direction from the extremity to the organs of the body.
The circulation of blood to and from the cells presents the greatest problem in the extremities of the body, such as the hands and feet, where the cells are located the greatest distance from the organs.
When blood is not appropriately circulated, the unnourished cells die. This can result in loss of the associated hand or foot.
In order to avoid amputation, it has long been known that circulation to these extremities must be enhanced particularly in old age. When for example, the femoral artery becomes blocked, it is advantageous to bypass this blockage in order to enhance the flow of blood to the lower leg and foot. In a common procedure, the saphenous vein is used for this purpose. Particularly when the blockage occurs in the upper region of the femoral artery, the saphenous vein can be harvested and reversed before attachment to the femoral artery above and below the blockage. This reversal of the vein orients the valves in a direction which facilitates a flow of blood toward rather than away from the extremities. This procedure for reversing the vein does not work as well in the lower regions of the femoral artery where the distal and proximal diameters of the artery and vein become incompatible.
Particularly for these lower regions, an in-situ procedure has evolved where the saphenous vein is left in place but its valves are disrupted in order to enhance a flow of blood in the reverse direction, toward rather than away from the extremity. In this procedure, the proximal end of the vein is attached to the proximal end of the artery, while the distal end of the vein is attached to the distal end of the artery. These similar ends are more compatible in size. When the valves are disrupted, the flow of blood in a reversed direction through the vein is enhanced to promote circulation to the extremity. Although conversion of the saphenous vein to an arterial function reduces the amount of venous conduit for return blood flow, it has been found that the remaining veins will typically be sufficient to accommodate the requirements of return blood flow.
This disruption of the valves is accomplished with an instrument referred to as a valvulotome. Although various valvulotomes have been used, they sometimes fail to adequately cut the valve in order to lower the resistance to downward blood flow.
One common variety of valvulotome is disclosed by Mehigan in U.S. Pat. No. 5,171,316. This instrument has a triangular head which offers no resistance to the undesirable engagement of sidebranches of the vein. The cutting edge is disposed at a 90.degree. angle to the axis of the vein and for this reason tends to cut a valve cusp from the inside out. This typically results in reduced cutting so that the valve cusp continues to form a cup thereby inhibiting blood flow in the reverse direction. In another valvulotome disclosed by Nobles in U.S. Pat. No. 5,026,383, a cutting tip including two prongs is used to engage two valve cusps from the downstream side of the valve. This instrument has had limited success since the cut of the cusps is typically limited to one-half the distance separating the prongs. Nevertheless, Nobles discloses that a scope can be positioned to view the cutting operation from the proximal side of the prongs, and a distal catheter can be connected between the prongs to facilitate movement of the valvulotome in the upstream direction.